[SRU] Large non-antialiased text causes xserver to abort

[Impact]
On certain affected hardware, results in X server crash when looking at certain kinds of large images.

[Development Solution]
Upstream fixed this bug in the 2.13.x version of -intel that we are shipping in natty.

[Stable Solution]
The attached patch is a cherrypick from the upstream tree that applies to the 2.12.x version of -intel in maverick. This patch is also the listed solution on the upstream bug report.

[Test Case]
On affected hardware, disable font antialiasing and load http://launchpadlibrarian.net/29956668/crash.html in firefox.
This will cause a segfault of the X server.

The fix will prevent this segfault from occuring, and instead firefox will display the words "GOODBYE WORLD!"

[Regression Potential]
Essentially none. This changes what happens when the uxa_pixmap_is_offscreen() call returns False. Before, it would fail the assertion test and terminate the X server. Pretty much any other behavior besides that is going to be an improvement!

That said, there are two subsequent commits on top of this one (which is why the patch in the description of this bug is different than that proposed). Near as I can tell these address other unrelated issues and so I'm omitting them for now. It is conceivable though that this patch provides an incomplete solution and those other patches should be backported too. But one step at a time; if this patch alone is sufficient to solve the issue it is the least risk way to go.

[Original Report]
Problem:
If I disable font antialiasing and attempt to access
http://launchpadlibrarian.net/29956668/crash.html in firefox my xserver aborts. This should not happen. The webpage should simply display the words "GOODBYE WORLD!" in very large text.

Note: text does not need to be very large. For example http://joe-editor.sourceforge.net/ also triggers the bug.

Description: Ubuntu 10.10
Release: 10.10

xserver-xorg-video-intel:
  Installed: 2:2.12.0-1ubuntu5.1
  Candidate: 2:2.12.0-1ubuntu5.1
  Version table:
 *** 2:2.12.0-1ubuntu5.1 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick-updates/main i386 Packages
        100 /var/lib/dpkg/status
     2:2.12.0-1ubuntu5 0
        500 http://gb.archive.ubuntu.com/ubuntu/ maverick/main i386 Packages

Backtrace:
#0 0x00681416 in __kernel_vsyscall ()
No symbol table info available.
#1 0x00298941 in raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
        resultvar = <value optimised out>
        pid = 3960820
        selftid = 1949
#2 0x0029be42 in abort () at abort.c:92
        act = {__sigaction_handler = {sa_handler = 0x468,
            sa_sigaction = 0x468}, sa_mask = {__val = {3966032, 120, 3965888,
              3960820, 3965888, 108, 3212918176, 3010141, 198339232, 3960820,
              3960820, 109, 3212918376, 2944968, 198339336, 198339336, 108,
              198339232, 0, 4222451712, 198339336, 198339437, 198339336,
              198339336, 198339444, 198339636, 198339336, 198339636, 0, 0, 0,
              0}}, sa_flags = 0, sa_restorer = 0x4}
        sigs = {__val = {32, 0 <repeats 31 times>}}
#3 0x002918e8 in __assert_fail (
    assertion=0x200098 "uxa_pixmap_is_offscreen(src_pixmap)",
    file=0x200080 "../../uxa/uxa-glyphs.c", line=986,
    function=0x200124 "uxa_glyphs_via_mask") at assert.c:81
        buf = 0xbd26c38 "X: ../../uxa/uxa-glyphs.c:986: uxa_glyphs_via_mask: Assertion `uxa_pixmap_is_offscreen(src_pixmap)' failed.\n"
#4 0x001ef988 in uxa_glyphs_via_mask (op=3 '\003', pSrc=0xbb11b58,
    pDst=0xbb366a8, maskFormat=0xb2bb7f0, xSrc=8, ySrc=77, nlist=1,
    list=0xbf814570, glyphs=0xbf814170) at ../../uxa/uxa-glyphs.c:986
        src_pixmap = 0xbd26440
        src_x = 0
        glyph = 0xbb34bb8
        src_y = 0
        priv = 0xbd26440
        screen = 0x9c01750
        mask = 0xbd26a48
        y = 52
        pixmap = 0xbd26938
        width = <value optimised out>
        dst_off_x = 6
        dst_off_y = 25
        box = {x1 = 6, y1 = 25, x2 = 145, y2 = 93}
        component_alpha = 0
        glyph_atlas = <value optimised out>
        x = 2
        height = <value optimised out>
        error = 0
#5 uxa_glyphs (op=3 '\003', pSrc=0xbb11b58, pDst=0xbb366a8,
    maskFormat=0xb2bb7f0, xSrc=8, ySrc=77, nlist=1, list=0xbf814570,
    glyphs=0xbf814170) at ../../uxa/uxa-glyphs.c:1151
        screen = 0x9c01750
        uxa_screen = <value optimised out>
        xDst = 2
        yDst = 198338872
        extents = {x1 = 0, y1 = 0, x2 = 0, y2 = 0}
        width = 0
        height = 0
        ret = <value optimised out>
        localDst = 0x8
#6 0x08122ae9 in damageGlyphs (op=6 '\006', pSrc=0xbb11b58, pDst=0xbb366a8,
    maskFormat=0xb2bb7f0, xSrc=<value optimised out>,
    ySrc=<value optimised out>, nlist=1, list=0xbf814570, glyphs=0xbf814170)
    at ../../../miext/damage/damage.c:718
        pScreen = <value optimised out>
#7 0x081bea90 in CompositeGlyphs (op=0 '\000', pSrc=0xbb11b58,
    pDst=0xbb366a8, maskFormat=0xb2bb7f0, xSrc=<value optimised out>,
    ySrc=<value optimised out>, nlist=1, lists=0xbf814570, glyphs=0xbf814170)
    at ../../render/glyph.c:604
No locals.
#8 0x0811c463 in ProcRenderCompositeGlyphs (client=0xb62e338)
    at ../../render/render.c:1435
        glyphSet = 0xb72e468
        pSrc = 0xbb11b58
        pDst = 0xbb366a8
        pFormat = 0xb2bb7f0
        listsLocal = {{xOff = 8, yOff = 77, len = 6 '\006',
            format = 0xb2bb7f0}, {xOff = 0, yOff = 0, len = 0 '\000',
            format = 0x0} <repeats 52 times>, {xOff = 24081, yOff = 2064,
            len = 0 '\000', format = 0x0}, {xOff = 0, yOff = 0,
            len = 0 '\000', format = 0x0}, {xOff = 0, yOff = 0,
            len = 0 '\000', format = 0xb62e338}, {xOff = 0, yOff = 0,
            len = 0 '\000', format = 0x0}, {xOff = 4084, yOff = 2079,
            len = 8 '\b', format = 0xb303cf0}, {xOff = 18536, yOff = -16511,
            len = 102 'f', format = 0x8202544}, {xOff = 0, yOff = 0,
            len = 136 '\210', format = 0x0}, {xOff = 0, yOff = 0,
            len = 0 '\000', format = 0x0}, {xOff = 14369, yOff = 2055,
            len = 0 '\000', format = 0x0}, {xOff = 0, yOff = 0,
            len = 244 '\364', format = 0xb62e338}, {xOff = 9536, yOff = 2080,
            len = 184 '\270', format = 0x8104a2e}}
        lists = 0xbf81457c
        listsBase = 0xbf814570
        glyphsLocal = {0xbb34bb8, 0xb9f2868, 0xb78ace0, 0xbaf1088, 0xbaf1088,
          0xbaf1088, 0x0 <repeats 250 times>}
        glyph = <value optimised out>
        glyphs = 0xbf814188
        glyphsBase = 0xbf814170
        buffer = <value optimised out>
        end = 0xba105b0 "\225\021\003"
        nglyph = -1082048120
        nlist = 1
        space = <value optimised out>
        size = <value optimised out>
        rc = <value optimised out>
#9 0x08118293 in ProcRenderDispatch (client=0x6) at ../../render/render.c:2051
No locals.
#10 0x0806e087 in Dispatch () at ../../dix/dispatch.c:432
        result = <value optimised out>
        client = 0xb62e338
        nready = 0
        start_tick = 260
#11 0x080625ba in main (argc=6, argv=0xbf814a04, envp=0xbf814a20)
    at ../../dix/main.c:291
        i = 1
        alwaysCheckForInput = {0, 1}

Tracked bug down to uxa/uxa-glyphs.c in the xserver-xorg-video-intel driver. I looked at the latest git of the driver and knocked together the following patch which seems to work. Not sure of the quality of the code though:

--- a/uxa/uxa-glyphs.c 2010-06-24 21:29:37.000000000 +0100
+++ b/uxa/uxa-glyphs.c 2010-12-31 19:51:49.000000000 +0000
@@ -164,8 +164,12 @@
             INTEL_CREATE_PIXMAP_TILING_X);
   if (!pixmap)
    goto bail;
- assert (uxa_pixmap_is_offscreen(pixmap));
-
+ if (!uxa_pixmap_is_offscreen(pixmap)) {
+ /* Presume shadow is in-effect */
+ pScreen->DestroyPixmap(pixmap);
+ uxa_unrealize_glyph_caches(pScreen);
+ return TRUE;
+ }
   component_alpha = NeedsComponent(pPictFormat->format);
   picture = CreatePicture(0, &pixmap->drawable, pPictFormat,
      CPComponentAlpha, &component_alpha,
@@ -780,9 +784,8 @@

     mask_pixmap =
      uxa_get_drawable_pixmap(this_atlas->pDrawable);
- assert (uxa_pixmap_is_offscreen(mask_pixmap));
-
- if (!uxa_screen->info->prepare_composite(op,
+ if (!uxa_pixmap_is_offscreen(mask_pixmap) ||
+ !uxa_screen->info->prepare_composite(op,
           localSrc, this_atlas, pDst,
           src_pixmap, mask_pixmap, dst_pixmap))
      return -1;
@@ -983,9 +986,8 @@

     src_pixmap =
      uxa_get_drawable_pixmap(this_atlas->pDrawable);
- assert (uxa_pixmap_is_offscreen(src_pixmap));
-
- if (!uxa_screen->info->prepare_composite(PictOpAdd,
+ if (!uxa_pixmap_is_offscreen(src_pixmap) ||
+ !uxa_screen->info->prepare_composite(PictOpAdd,
           this_atlas, NULL, mask,
           src_pixmap, NULL, pixmap))
      return -1;

---
Architecture: i386
CurrentDmesg: [ 36.408005] eth0: no IPv6 routers present
DRM.card0.DisplayPort.1:
 status: disconnected
 enabled: disabled
 dpms: Off
 modes:
 edid-base64:
DRM.card0.DisplayPort.2:
 status: disconnected
 enabled: disabled
 dpms: Off
 modes:
 edid-base64:
DRM.card0.HDMI_Type_A.1:
 status: disconnected
 enabled: disabled
 dpms: Off
 modes:
 edid-base64:
DRM.card0.HDMI_Type_A.2:
 status: disconnected
 enabled: disabled
 dpms: Off
 modes:
 edid-base64:
DRM.card0.VGA.1:
 status: connected
 enabled: enabled
 dpms: On
 modes: 1280x1024 1280x1024 1280x960 1152x864 1024x768 1024x768 1024x768 832x624 800x600 800x600 800x600 800x600 640x480 640x480 640x480 640x480 720x400
 edid-base64: AP///////wBA5QYXlxMAABcPAQMMIht4LgyVolZMliUaUFS/74CBgIFAcU8AAAAAAAAAAAAAMCoAmFEAKkAwcBMAUg4RAAAeAAAAAAAAAAAAAAAAAAAAAAAAAAAA/QA4Sx9RDgAKICAgICAgAAAA/ABHTlIgVFM3MDAKICAgAJE=
DistroRelease: Ubuntu 10.10
DkmsStatus:
 virtualbox-ose, 3.2.8, 2.6.35-24-generic, i686: installed
 virtualbox-ose, 3.2.8, 2.6.35-23-generic, i686: installed
 virtualbox-ose, 3.2.8, 2.6.32-26-generic, i686: installed
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release i386 (20091028.5)
MachineType: System manufacturer System Product Name
Package: xserver-xorg-video-intel 2:2.12.0-1ubuntu5.1 [modified: usr/lib/libI810XvMC.so.1.0.0 usr/lib/libIntelXvMC.so.1.0.0 usr/lib/xorg/modules/drivers/intel_drv.so]
PackageArchitecture: i386
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.35-24-generic root=UUID=8dc60281-9b37-44b9-98fe-54ce9f16b232 ro quiet splash
ProcEnviron:
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.35-24.42-generic 2.6.35.8
Tags: maverick maverick maverick maverick maverick maverick
Uname: Linux 2.6.35-24-generic i686
UserGroups: adm admin cdrom dialout lpadmin plugdev sambashare video
dmi.bios.date: 09/04/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 0204
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: V-P5G45
dmi.board.vendor: ASUSTeK Computer INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Asset-1234567890
dmi.chassis.type: 3
dmi.chassis.vendor: Chassis Manufacture
dmi.chassis.version: Chassis Version
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr0204:bd09/04/2008:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKComputerINC.:rnV-P5G45:rvrRev1.xx:cvnChassisManufacture:ct3:cvrChassisVersion:
dmi.product.name: System Product Name
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer
system:
 distro: Ubuntu
 codename: maverick
 architecture: i686
 kernel: 2.6.35-24-generic